System for measuring rotor blade vibration

ABSTRACT

A system for measuring rotor blade vibration in a compressor or turbine in which magnetic type sensors are positioned at selected points about the periphery of the rotor to produce pairs of signals generated by passing blades. These signals are then phase compared and a voltage obtained which is indicative of whether one signal leads or lags another and the magnitude of the lead or lag.

United Stat Robinson [54] SYSTEM FOR MEASURING ROTOR BLADE VIBRATION[72] Inventor:

Tullahoma, Tenn. 37388 [22] Filed: Oct. 2, 1970 [21] Appl.No.: 77,628

Raymond A. Robinson, Lake Circle Drive,

[151 3,654,803 [451 Apr.11,1972

3,289,073 11/1966 Loefiler ..73/71.4X

Primary Examiner-James J. Gill Attorney-C. A. Phillips ABSTRACT A systemfor measuring rotor blade vibration in a compressor or turbine in whichmagnetic type sensors are positioned at selected points about theperiphery of the rotor to produce [52] U.S. CL .L ..73/71.4 pairs ofsignals generated by passing blades. These signals are [51] Int. Cl...G0lh 11/00 then phase compared and a voltage obtained which is indica-[58] Field of Search ..73/67, 70, 71.4 tive of whether one signal leadsor lags another and the magnitude of the lead or lag. [56] ReferencesCited 11 Claims, 19 Drawing Figures UNITED STATES PATENTS 3,058,33910/1962 Shapiro ..73/71.4

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' SELECTOR SYSTEM FOR MEASURING ROTOR BLADE VIBRATION BACKGROUND OF THEINVENTION This invention relates to the detection of vibration in axialflow turbines or compressors and particularly to a measurement system inwhich vibrations are detected by the comparison of waveforms generatedby a selected pair of blades passing a pair of magnetic pickups whichare spaced to symetrically sense the movement of blades passing thepickups.

It has been previously established that blade vibration of rotarycompressors and turbines often forewam of rotor failure and possibledestruction of all of the blades in the compressor or turbine in whichthe vibrations are detected. It is therefore of acknowledged importancethat some means be available to monitor rotor blade vibration.

SUMMARY OF THE INVENTION It is an object of the present waveformsprovide an improved system for measuring and comparing relativevibratory motion between rotor blades of a turbine or compressor.

In accordance with the invention, magnetic pickups are positioned on theperiphery of a turbine or compressor, with at least two of thempositioned to simultaneously detect the passage of a pair of selectedblades. The magnetic pickups are separated by the distance between theblades being observed and the signals from these pickups, which assensed, approximate a cycle of an alternating current wave, aretranslated into rectangular pulses in a manner which preserves theirtime identity. They are then time or phase compared and an electricaloutput produced which indicates by way of polarity which of the signalsleads in time the other, if such is the case, and indicates, inmagnitude, the extent of this lead or lag.

These and other objects, features and advantages waveforms inventionwill become more apparent from the following description and claims whenconsidered together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a overall schematic diagramof an embodiment of the invention;

FIG. 2 is a diagrammatic illustration of the blade-magnetic pickuprelationships at three stages of rotation of the turbine referred to inFIG. 1;

FIG. 3 is a diagram illustrating oscilloscope patterns provided as anoutput of the systems shown in FIG. 1;

FIG. 4 is an electrical schematic diagram of one of the three identicalpulse shapers shown in FIG. 1 and which functions to convert magneticinput signals into precisely timed-related pulse signals;

FIG. 5 shows a series of waveforms illustrating the operation of thepulse shaper of FIG. 4;

FIG. 6 is an electrical circuit diagram of a switch control shown inFIG. 1 and which develops timing pulses related to the position ofturbine blades with respect to magnetic pickups which sense theirpassage; blade FIG. 7 is a timing chart showing waveforms generated bythe primary counter of the switch control shown in FIG. 1;

FIG. 8 is a timing chart showing waveforms generated by the secondarycounter of switch control shown in FIG. 1;

FIG. 9 is a timing chart showing waveforms generated by the secondarycounter control of the switch control shown in FIG. 1;

FIG. 10 is a timing chart of waveforms developed by the logic selectorcircuit of the switch control shown in FIG. 1;

FIG. 11 is an electrical schematic diagram of the switching circuitshown in FIG. 1 which functions to receive magnetic pickup signals andtiming pulses and provides as outputs two selected signals for analysis;

FIG. 12 is a timing chart illustrating the operation of the switchingcircuit shown in FIG. 11;

FIG. 13 is an electrical schematic circuit diagram of the manualselector shown in FIG. 1 which functions to step or add a count to theprimary counter of the switch control shown in FIGS. 1 and 6 thereby tochange the selection of blades being observed;

FIG. 14 is a timing chart illustrating the operation of the manualselector shown in FIG. 13;

FIG. 15 is an electrical schematic circuit diagram of the phase detectorshown in FIG. 1 which functions to time or phase compare two input bladesignals and to provide an electrical output of a polarity indicatingwhether one signal leads or lags the other and of a magnitude indicatingthe magnitude of the lead or lag; in addition the phase detectorprovides a stepped voltage output which identifies in time a particularmeasurement out of a series of measurements being made during a givenrevolution of the turbine;

FIG. 16 is a timing chart illustrating waveforms generated in thevoltage selector shown in FIG. 15;

FIG. 17 is a timing chart illustrating the waveforms appearing in thesweep circuit shown in FIG. 15;

FIG. 18 is a timing chart illustrating waveforms appearing in the rastercircuit shown in FIG. 15; and

FIG. 19 is an electrical schematic circuit diagram of an alarm systemwhich is energized when a critical vibratory condition is sensed by thesystem.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to FIG. 1,magnetic pickups P1, P2, P3 and P4 are positioned about the periphery ofturbine 1. Turbine l is of the type in which gas flow is axial. Thepickups are equally spaced about one quarter of a wavelength apartaround the circumference of turbine l as calculated from known naturalfrequencies of vibration of the blades generally designated. As shown,two blades are between the blades opposite pickups. They are positionedso that the trailing edge of two blades, for example, blades B2 and B52will be opposite pickups (pickups P1 and P2 as shown), at a particulartime. An additional magnetic pickup, pickup PC, which serves as acontrol signal pickup, is located so that when a blade of rotor 20 ofturbine 1 is opposite it, blades are not over any of the other fourpickups.

In order to best observe and detect vibration, the magnetic pickupsspacings, two blades between the two being observed, is based upon thenatural frequency of the turbine, and in terms of this frequency arespaced A4 wavelengths apart. FIG. 2 shows in three progressive diagramsinstantaneous rotor positions for three comparative measurements withrespect to Blades 2 and 52, as turbine 1 rotates from the first position2A to the second position 2B and from the second position to the thirdposition 2C.

The outputs from pickups P1, P2, P3, P4 and PC associated with turbine lare fed to turbine selector 24 as are similar sets of outputs from otherturbines, illustrated by turbines 2 and 3 on FIG. 1. Turbine selector 24is a switch which makes available as selected, sets of magnetic pickupoutputs, outputs to switching circuit 28 and, through pulse shaper 30,to switch control 32. As an aid in signal tracing, signal designationsare in lower case letters and opposite numerals designate the outputs.Pulse shaper 30 amplifies the incoming pulses PC and provides arectangular pulse output which is initiated at a predetermined point onthe magnetic pickup signal and the pulse output is of a fixed width. Thepulse serves as a trigger pulse which is applied to switch control 32where it is fed to primary counter 34, secondary counter 36 andsecondary counter control 38. Primary counter 34 functions to count N- 1pulses, there N is the number of turbine blades. Secondary counter 36functions to count to 3 (the distance of blade travel from one pickup toanother in terms of blade width) twice in succession each revolution,and secondary counter control 38 counts the number of times thatsecondary counter 36 counts the number of blades between pickups andresets secondary counter 36 after allowing secondary counter 36 to gothrough two counting sequences each revolution of turbine 1. Manualselector 40 functions to step primary counter 34 to cause the pairdirectly behind the pair of blades then being ob-

1. A system for measuring rotor blade vibration in a turbine, or compressor, comprising: A. a plurality of sensors positioned in spaced relation around and in close proximity to said blades of a said turbine or compressor, each sensor comprising means for providing an electrical output which is a function of blade motion with respect to a said sensor; B. switching means responsive to outputs of said sensors for selectively providing first and second blade signal outputs, simultaneously, corresponding to outputs of first and second of said sensors and responsive to the passage of a selected pair of blades by said first and second of said sensors; C. phase detection means responsive to said outputs of said switching means for providing an output potential of an amplitude and polarity which is a function of any lead or lag of one blade signal output with respect to another blade signal output simultaneously observed; and D. indicating means responsive to said phase detection means for indicating the lead or lag of one blade signal output with respect to another and for indicating the magnitude of any such lead or lag.
 2. A system for measuring rotor blade vibration as set forth in claim 1 wherein said phase detection means comprises: A. voltage selection means responsive to said first and second blade signal outputs of said switching means for providing a first polarity signal when said first output leads in phase said second output and providing a second and opposite polarity signal when said first output lags said second output; and B. phase comparison means responsive to said first and second outputs of said switching means for providing a third output signal which is function of the time difference or phase of said first and second outputs of said switching means.
 3. A system for measuring rotor blade vibration as set forth in claim 2 wherein said phase detection means further comprises output means responsive to the output of said voltage selection means and phase comparison means for providing an electrical output which is of a polarity which is a function of the polarity of said voltage selection means and of a duration which is a function of the output of said phase comparison means.
 4. A system for measuring rotor blade vibration as set forth in claim 3 wherein said output means comprises means for generating a sawtooth wave.
 5. A system for measuring rotor blade vibration as set forth in claim 4 wherein: A. said switching means comprises means for providing a series of sets of said first and second blade signal outputs in sequence representative of observations of a particular pair of blades at a plurality of positions during a cycle of rotation of a said compressor or turbine; and B. said phase detection means further comprises signal identification means responsive to each said set of blade signal outputs for providing an identifying and discrete voltage output coincident with the occurrence of a said set of blade signal outputs whereby each set may be identified.
 6. A system for measuring rotor blade vibration as set forth in claim 5 wherein said indicating means comprises an oscilloscope having first axis control means connected to and controlled by the output of said output means of said phase detection having second axis control means connected to and controlled by the output of said signal identification means whereby discrete traces are generated on said oscilloscope for each said set of blade signal outputs.
 7. A system for measuring rotor blade vibration as set forth in claim 2 further comprising pulse shaping means in series between a said sensor and said phase detection means for providing an output pulse of One polarity which is of fixed width and which commences at an identical level point on the leading edge of each output of a said sensor.
 8. A system for measuring rotor blade vibration as set forth in claim 7 wherein each said pulse shaper comprises: A. a first voltage comparator having first and second inputs and an output and includes a diode connected between said first input and said output, whereby said output is prevented from going lower in value than said first input; B. a reference voltage of the polarity of the input of said first input being applied to said second input of said first comparator; C. a second voltage comparator having first and second inputs and an output and includes a diode connected between said last named first input and said last named output, whereby said last named output is prevented from going lower in value than said last named first input; D. a zero reference voltage being applied to said second input of said second comparator; E. first and second NOR gates, a first input of said first NOR gate being connected to the output of said first comparator, the first input of said second NOR gate being connected to the output of said second comparator, the second input of said second NOR gate being connected to the output of said first NOR gate and the second input of said first NOR gate being connected to the output of said second NOR gate; and a one shot multi-vibrator being connected to the output of said second NOR gate; Whereby an alternating current signal applied to said first input of said comparator provides a rectangular pulse output.
 9. A system for measuring rotor blade vibration as set forth in claim 6 further comprising alarm means responsive to the level of output of said electrical output of said phase detection means for providing a signal whenever a predetermined level occurs.
 10. A system for measuring rotor blade vibration as set forth in claim 9 further comprising at least one additional said turbine and plurality sensors related thereof, and including turbine selection means for selectively interconnecting the sensors related to a particular said turbine to said switching means.
 11. A system for measuring rotor blade vibration as set forth in claim 10 wherein said alarm means comprises means responsive to said turbine selection means for indicating the particular turbine being monitored. 